1. Field of the Invention
The present invention relates to an auto focusing control technique of a camera, and more particularly to a method for controlling auto focusing of a camera for variably selecting a wobbling width in accordance with the position of a zoom lens and opening of an iris.
2. Description of the Prior Art
A technique for controlling auto focusing of a camera is to detect a subject by using a luminance signal of the subject that is picked up via a camera lens, and driving an optical system to be fitted to the detected subject, thereby automatically adjusting its focus. FIG. 1 schematically illustrates a circuit construction for controlling auto focusing of a camera.
Here, an optical system 10 includes an objective lens 10a, a zoom lens 10a, an iris 10c and a focusing lens 10d, and a photoelectric converting unit, i.e. CCD 20, converts an image of a subject picked up via optical system 10 into an electric signal. Additionally, an automatic gain controlling (hereinafter simply referred to as xe2x80x9cAGCxe2x80x9d) circuit 30 carries out automatic gain controlling of a video signal converted by photoelectric converting unit 20. A digital signal processing section 40 digitizes the AGC-processed video signal and separates it into a luminance signal and a chrominance signal to process the obtained signals, and an evaluation value detecting section 50 detects an evaluation value for the focusing controlling by using the luminance signal separated in digital signal processing section 40. In addition to these, a controlling section 60 judges whether the subject is detected or not by means of the evaluation value detected in evaluation value detecting section 50 and provides a focusing area control signal and an optical system driving control signal in accordance with the result of the determination, and a focus motor driving section 70a receives the lens driving control signal from controlling section 60 to provide a focusing lens driving signal. A focus motor 80a drives focusing lens 10d in response to the focus motor driving signal, and an iris motor driving section 70b receives an iris driving control signal from controlling section 60 to provide an iris motor driving signal. Also included are an iris motor 80b for driving iris 10c in accordance with the iris motor driving signal, and a zoom motor driving section 70c for receiving a zoom driving control signal from controlling section 60 to provide a zoom motor driving signal. Further to these, a zoom motor 80c drives zoom lens 10b in accordance with the zoom motor driving signal, an exposure detecting section 90 detects the opening of iris 10c to supply it into controlling section 60, and a zoom position detecting section 100 detects the position of zoom lens 10b to supply it to controlling section 60.
The image picked up by optical system 10 is converted into the electric video signal in photoelectric converting unit 20 via objective lens 10a, zoom lens 10b, iris 10c and focusing lens 10d. Then, the obtained video signal is automatically gain-controlled by AGC circuit 30 to be supplied into digital signal processing section 40.
Digital signal processing section 40 converts an input analog video signal into a digital signal, and separates the digital video signal into luminance signal Y and chrominance signal C. Thus, separated chrominance signal C is processed via a chrominance signal processor (not shown), and luminance signal Y is processed via a luminance signal processor (not shown), thereby providing a composite video signal CVS.
At this time, evaluation detecting section 50 receives the processed luminance signal to supply a luminance signal evaluation value of the subject image to controlling section 60 which in turn performs the control, such as auto focusing and auto exposure, based on the evaluation value supplied.
In the conventional auto focusing technique, however, the transferring speed and wobbling width of the focus lens are determined unrelated to a depth of focus.
Here, the depth of focus FNO is defined by an equation FNO=f/D (where f denotes a focal length by the zoom, and D denotes a diameter of the employed lens in accordance with the iris opening), which has a proportional relation to the iris opening.
That is, the larger the iris opening, the lower the depth of focus. Whereas, the smaller the iris opening, the larger the depth of focus.
But the wobbling width and lens transferring speed were heretofore controlled regardless of the depth of focus in the conventional auto focusing controlling technique.
More specifically, as shown in FIG. 2, focus motor 80a is controlled via focus motor driving section 70a by the wobbling width which is fixed to an optional focus position to drive focusing lens 10d, thereby deciding the auto focusing direction. Then, after focusing lens 10d is driven to be matched to the decided direction to track until reaching a peak point mode, the focus position is set at a peak point Zo at which the detected luminance signal evaluation value becomes decreased after being increased.
When the focusing operation is performed in the conventional auto focusing controlling technique, the focus lens speed is heretofore determined by the fixed wobbling width unrelated ti the depth of focus to thereby involve distinctive hunting phenomena in case of a low depth of focus.
The objects of the present invention are to overcome problems and disadvantages of the conventional method for controlling camera autofocusing
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
A first object of the present invention is to provide a method for controlling auto focusing of a camera, wherein an iris opening and a zoom position are detected to select a variable wobbling width in accordance with the result of the detection for preventing the hunting associative with a state of a depth of focus and enabling a quick auto focusing operation.
A second object of the present invention is to provide a method for controlling auto focusing of a camera, wherein an iris opening and a zoom position are detected to select a variable wobbling width in accordance with the result of the detection. An iris is controlled to allow the selected wobbling width to have a preset reference value prior to performing am auto focusing operation, thereby preventing the hunting and enabling a quick auto focusing operation.
A third object of the present invention is to provide a method for controlling auto focusing of a camera, wherein an iris opening is detected to have a preset reference value by controlling an iris. A variable wobbling width is selected in accordance with the result of the detection for performing an auto focusing operation, thereby preventing the hunting and enabling a quick auto focusing operation.
To achieve the first object of the present invention, the first embodiment of the present invention provides a method for controlling auto focusing of a camera, which is performed by detecting an opening of an iris and a zoom position of a zoom lens, and selecting a wobbling width based on the detected iris opening and zoom position. Thereafter, transferring a focus lens based on the selected wobbling width is carried out.
To achieve the second object of the present invention, a second embodiment of the present method detects an opening of an iris and a zoom position of a zoom lens and selects a first wobbling width based on the detected iris opening and zoom position. The selected first wobbling width is compared with a reference value, and the opening of the iris is controlled to a new opening in accordance with a result of the comparison. A second wobbling width corresponding to the new opening is selected, and a focus lens is transferred based on one of the selected first and second wobbling widths in accordance with the result of the comparison.
In order to achieve the third object of the present invention, the third embodiment of the present method detects an opening of an iris and compares an iris value representing the detected opening of the iris with a predetermined reference value. The opening of the iris is adjusted in accordance with a result of the comparison. A zoom position of a zoom lens is detected when the adjusted iris opening exceeds the reference value, and a wobbling width is selected based on the adjusted iris opening and the detected zoom position. A focus lens is transferred based on the selected wobbling width.
In the above-described embodiments, the step of selecting the wobbling width may be performed by selecting any one among a plurality of wobbling widths previously stored in a memory corresponding to a depth of focus based on the iris opening and zoom lens position.
Preferably, the plurality of wobbling widths may have at least a first wobbling width selected when the iris opening is large and zoom position is close, a second wobbling width selected when the iris opening is small and zoom position is close or selected when the iris opening is large and zoom position is remote, and a third wobbling width selected when the iris opening is small and zoom position is remote.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.